The invention relates to a method for influencing the geometry of a rolled item in a controlled manner, said rolled item being transformed from an initial state into an intermediate or final state by rolling with the aid of a rolling stand by at least one processing assembly. The invention further relates to an open-loop and/or closed-loop control device, a machine-readable program code and a data medium.
All of the systems required to produce rolled products can be combined in a rolling mill. A distinction is made between hot-rolling mills and cold-rolling mills, depending on the type of forming. In hot-rolling mills or hot-rolling broad-strip mills, roughed slabs or ingots, usually referred to simply as slabs, are processed into hot strip. This hot working is one of the methods which follow the primary forming (ingot casting, continuous casting). The rolled item is heated to temperatures up to 1,350° C. in this case, and reduced to a predetermined thickness in a roll gap of the rolling mill by pressure while preferably remaining above its recrystallization temperature. Since the finished product (usually steel or aluminum strip) can rarely be rolled out in a single pass, a plurality of rolling stands are combined to form a mill train in which a plurality of reduction stages are performed according to the number of stand passes. In hot-rolling mills, a distinction is made between a roughing train and a finishing train, the slab being preprocessed in the roughing train before then being rolled out to its final dimensions in the finishing train, which usually comprises five, six or seven stands.
One of the problems that occurs when rolling slabs, or the strips derived therefrom, is that the item to be rolled in a roughing train has a thickness curve across its width. The purpose of rolling is usually to produce strips which at the end of the finishing train have not only a thickness across their width which is substantially symmetrical relative to the strip center, i.e. an absence of taper, but also minimal deformation along the length of the rolled item, i.e. an absence of strip saber.
However, this is difficult to achieve if an item to be rolled already has a tapered shape when rolled for the first time within the hot-rolling mill train. The taper of the rolled item is generally caused by the casting process and the subsequent cooling and further processing, in particular halving, of the cast slabs. If a tapered rolled item must then be rolled out into a slab having a substantially rectangular cross section, the volume retention causes greater material flow (in particular longitudinal flow) on the “thick” side of the slab than on the “thin” side of the slab. This differing material flow in a longitudinal direction of the rolled item results in the formation of a longitudinal curvature or strip saber. Depending on the nature of the strip saber, a rolled item having longitudinal curvature can result in difficulties during subsequent processing of the rolled item. The formation of the strip saber may be so pronounced that further processing of the rolled item is impossible.
Various methods are customarily used to deal with a taper or longitudinal curvature of a rolled item in a mill train. These methods are generally based on an asymmetrical distribution of tension at the roll gap, wherein a force is generated transversely relative to the direction of rolling.
Position-controlled processing assemblies for applying a transverse force are also known, e.g. lateral guides as described in WO2006/119984 or vertical stands (so-called edgers) for width control.